It saddens me to see two people sharing a single set of earbuds, one lonely channel per listener. What if there were an app that let one person broadcast music to the mobile devices of nearby friends? Add voice and text chat, plus some ways to monetize the service through DSP plug-ins, hardware add-ons, and referral fees for promoting music.

What are the requirements, and what types of businesses could result?

Failing that, how about some really immersive headphones?